The research is focused on defining the cellular and molecular biology of the hepatic and pancreatic stem cell compartments in normal and neoplastic organs with a particular emphasis on the role of growth factors and cytokines. The present study was undertaken to determine whether the immature bile epithelium responds differently to growth stimulus induced by bile stasis to that seen in the adult animal. In addition, the possible involvement of the growth factor/receptor systems associated with early activation of hepatic stem cells in bile duct proliferation was examined. Alpha-fetoprotein was highly and selectively expressed in small bile ducts 7 days after bile duct ligation in young rats up to 5 weeks of age. Although no significant increase in the expression of stem cell factor, c-kit, hepatocyte growth factor and transforming growth factor-alpha is observed in adults rats, the expression of all these growth factors was increased in the bile duct ligated rat up to 5 weeks of age. These results indicate that the bile epithelium in young rats responds to bile stasis in a fashion that is phenotypically similar to that seen during early activation of hepatic stem cells in adult liver.